The present invention relates to an automatic brake control system for controlling the running speed of a vehicle automatically.
As this type of an automatic brake control system there is known the system described in Japanese Patent Laid Open No. 71727/87.
In such automatic brake control system, the distance between a front obstacle such as a vehicle and a vehicle to be controlled is detected and the vehicle to be controlled is braked on the basis of the result of the detection. In the case where the distance from the obstacle is judged to be sufficient for safe running on the basis of the result of comparison between a reference running speed which is determined from a vehicular running speed at the start point of the braking and a vehicular running speed during the above braking operation, the braking is released.
In such prior art, however, in many cases there occurs discrepancy between the braking action and the actual driving sense.
More particularly, in a conventional automatic braking system, braking is not performed as long as the distance up to a front vehicle does not reach a predetermined distance, on the basis of only the running speed of a vehicle to be controlled (hereinafter referred to as "this vehicle"), irrespective of whether the running speed of the front vehicle is high or low, if only the running speed of this vehicle is constant.
Consequently, in the case where the running speed of the front vehicle is sufficiently high and the front vehicle and this vehicle are in a relation such that the distance between both vehicles becomes smaller gradually, braking is performed with a sufficient time margin, but when the front vehicle is braked suddenly or is at a standstill, there is little time margin, thus causing a danger of rear-end collision.
Conversely, if a braking start distance is determined, premising sudden braking or stopping of the front vehicle, the braking will be started in a too early stage, causing a danger against a succeeding vehicle rather than this vehicle, even when vehicles are running smoothly and the running speed of the preceding vehicle is sufficiently high.
The present invention has been accomplished in view of the above-mentioned problem and it is the object of the invention to provide a technique which permits a braking operation to be performed in a state closer to the actual driving sense in an automatic brake control system.